Multiple wave oscillator with selfadjusting grid excitation



A. SENAUKE' 2,186,434

MULTIPLE WAVE OSCILLATGR wiTH SELF -ADJUSTING GRID EXCITATION Filed March 30, 1938 ATToRNEvsy Patented Jan. 9, 1940 UNITED S ATE MULTIPLE WAVE OSCILLATOR wrrn SELF- ADJUSTING GRID-EXCITATION Alexander Senauke, New York, N. Y., assignor to AmpereX Electronic Products, Inc., Brooklyn, N. Y., a corporation of New York Application March 30,

7 Claims.

of power-driven oscillating circuits for generat-' ing oscillatory current, energized by a direct current source, orpower frequency alternating current source, and to apparatus which is especially useful as a high frequency generator in diathermy machines, although, as will be understood, it may be employed under many other circumstances where an oscillator is desired which will furnish oscillating current of a multiplicity of frequen cies.

Among the objects of my invention may be mentioned the following:

To provide multiple-frequency generating apparatus in which the frequency of the oscillations generated may be selectively controlled'by changing the constants of one circuit only .of the apparatus; for'example, in a circuit utilizing a tuned grid, tuned plate push-pull oscillator, by changing the constants of the plate circuit only.

To provide means for automatically providing the proper degree or amount of grid excitation for any of a multiplicity of wave lengths (or frequencies) which may trolled by the wave length switch.

To provide oscillation generating apparatus which may be assembled and adjusted at the factory in such a manner that it is capable'of operation by those adjustment of by them in the adjustment of the apparatus to various wave lengths and that the same'willoperate properly.- I

Still other objects and advantages of myinvention will be apparent from the specification.

In this application I have particularly pointed out and distinctly claimed-the part, improvement,

or combination which I claim as my inventionor discovery, and I have explained the principles thereof, and the best mode in which I'have contemplated applying that principle, so as todis-Q tinguish it from other inventions.

In the drawing: r Fig. 1 is a circuit diagram of apparatus accord,- ing to my invention for furnishing oscillations on either of two wave lengths as desired, and

. Fig. 2 is a similar diagram of an oscillator for furnishing oscillations on any one of three wave lengths.

Referring now toFig. lof the drawing, I have illustrated a vacuum tube oscillator employing two vacuum tubes, preferably, although not necessarily, of the triode type connected in pushpull,.the circuit being of the tuned grid, tuned be desired inoperation, as 'conv unskilled in the manipulation and i such apparatus, with the assurance that no technical problemswill be encountered it willbe understood that "inductances 3, 4 and 5 will 1938, Serial No. 198,890

plate or so-called TNT type. tubes 1 and 2 respectively comprises a. cathode, a control electrode and an anode illustrated as filamentary cathode la, grid lb, and plate la in tube I and filament 2a, grid 21) and plate "20 in tubeqZ. The filaments may be connected together in parallel operation as indicated, and for simplicity I have omitted the filament heating source, the same being well knownto the art. v

The anode or plate lc may be connected through inductance 3 to one terminal of inductance 5. Similarly the anode or plate 20 may be connected through inductance 4 to the other terminal of inductance 5, the mid-point .of which may be connected to a suitable source ofpotential for energizing the plate circuit, herein indicated as l2. I

- The grid lb may be connected through inductance Ito a tuned circuit which may comprise inductance l0 and capacity I Land the grid 2b may be connected through inductance 8 to the opposite side of said tuned circuit. The grid circuit may be completed by a connection from the midpoint of inductance I0 through resistance 9 to a point on the filament circuit.

The opposite terminals of inductance 5 maybe connected to the terminals of a switch l3 by the operation of which the inductance 5 may be short circuited. The same is shown in diagrammatic form with an arrow indicating closure ofthe switch to short circuit the said inductance. Preferably inductances 3 and 4 are both arranged at right angles with inductance 5 so as to have minimum magnetic coupling therewith.

In case the tubes are of the simple triode type, the feedback required Each of these I to sustain oscillation takes place through the internal capacity of the tube and hence no separate feedback means is shown; although in case other types of tubes are employed, it will be understood that other forms of feedback circuits may be employed such as are well understood in the art.

In diathermy ma able to supply at least two frequencies of oscillation. The lower frequency may be, for example, in the neighborhood of 20 megacycles (15 meters) the higher frequency in the neighborhood of 50 megacycles (fimeters) that the natural frequency of the plate circuit with the tubes associated'therewith is close to the desired lower frequency, necessary to be explained in the art.

hines it is ordinarily desir I In this case the values of preferably be so chosen this being a matter not in detail to those skilled The grid circuit for maximum eniciency will preferably be tuned to a somewhat higher frequency than the plate circuit although not greatly higher, it being understood, as will be clear to those skilled in the art, that the grid circuit should have an inductive reactance of sufficient magnitude to produce the necessary grid voltage in the proper phase to keep the oscillatory circuit, which in this case is the plate circuit, in oscillation.

Considering the operation of the circuit, for example, at 15 meters, the switch and the inductances, 3, 4', and 5 in the plate circuit. Since the switch 13 does not operate on the grid circuit in any way, the entire grid circuit will be includedin It should be noted that the constants of inductances I and 8 are such that these coils alone are too small to provide the necessary excitation at- 15 meters, but when added to the inductive reactance of the LC circuit formed by inductance I0 and capacity II, the combined impedance is sufiicient to give the necessary excitation; that is to say, neither coils 1', 8 or III] (with condenser II in shunt with the latter) alone are suficient to give the proper excitation at 15 meters. However, all together will afford such excitation, this result being obtained, by a proper choice of the values of inductances 1 and 8 and by choice of the values of inductance I0 and condenser II to supplement the reactance of inductances 1 and 8 at the lower frequency.

For operation at the higher frequencies the switch I3 may be closed, short-circuiting inductance 5, the valuebeing so chosen that the natural frequency of the plate circuit with inductance 5 short-circuited and with the tubes in circuit is now very close to the higher frequency desired, in this instance megacycles'. Under such circumstances, if the values of the inductance I0 and capacity I I are properly chosen, capacity II will operate substantially as a by-pass around inductance I0, and, although the impedance of the LC circuit made up of inductance I0 and capacity I! may be negative, that is to say, in the wrong phase to sustain oscillation, the impedances of the inductances 1 and 8 is in the proper phase and is made sufficient to compensate for the negative (in sign) impedance of the LC' circuit, if such is the case.

I- have found that very satisfactory results are obtained when the tubes I and 2 are of the type commercially available on the market as I-IF200, when inductances 1 and 8 have an inductance of 0.4 microhenry, when resistance 9 has the value, of 5000 ohms, inductance Iuan inductance of 1.0 microhenry, condenser I I a capacity of 50 micromicrofarads, inductances 3 and 4, 0.8 microhenry, and inductance '5, 9.0 microhenries.

With the apparatus shown and described, it will be clear that with the switch in position so thatinductance 5 is not short-circuited, the oscillator will generate oscillations of lower frequency as determined by the constantsof the plate circuit, and that the proper excitation will be'suppliedby the grid circuit, the inductive impedance of inductances 1 and 8 being supplemented by that of the LC circuit II], II. When the switch I3 is thrown in position to short-circuit the inductance 5, the constants of the plate circuit will be modified to cause a higher frequency tobe generated, and in this instance the excitation again will be supplied in proper degree I3 will be openwill be included either adjustment.

of inductances 3 and t so'that the plate voltage fed back to the grid, is

of the correct phase efficient oscillation.

It will be understood that while I have shown and magnitude to maintain selecting the constants of the plate circuit by connection or short-circuiting of inductance, one may add or subtract capacity in parallel in the plate circuit for the purpose of controlling the constants thereof, as will be understood by those skilled in the art.

The same principle may be applied in oscillators designed to deliver oscillations of more than two frequencies. A circuit for this purpose is shown in Fig. 2 in which like reference numerals indicate like parts as in Fig. 1. In this instance the circuit is much the same as that of Fig. 1 except that an additional set of grid inductances I l and I5 is provided, with condenser It connected between the common terminals of coils I 4 and 1 and S5 and 8 respectively, and with an additional pair of coils 16 and I1 in the plate circuit. Connections are provided from the common point of coils I3 and It to switch contact 59, andfrom the common point of coils 4 and I1 to switch contact 26. In this instance switch I3 is indicated diagrammatically as being movable from neutral position to connect contacts I9 and 20 together in one position and to connect the other pair of contacts in the other position. The operation is the same in principle as a1- ready'described for Fig. 1. In this instance, for example, it may be desiredto generate oscillations of 80 meters, 15 and 6 meters, respectively, and the plate circuit constants are so chosen that when the switch I3 is in neutral position, the oscillatory plate circuit with the tubes associated therewith oscillates on the lowest frequency desired. The constants of the grid circuit are so chosen that proper grid excitation is supplied no matter what the position of the wave change switch I 3. In this instance the inductances of coils 1, I4, 8 and 15 are insufiicient to supply proper grid excitation at the lowest frequency and this lack of excitation is made up by the LC circuit of inductance I0 and capacity H, which preferably is so chosen as to have a relatively high capacity and a relatively low inductance for the particular frequency desired.

When oscillations of the next higher frequency are desired, the wave change switch may be moved to the left to short-circuit inductance 5 and the frequency will now be determined by the constants of the plate circuit (with the tubes associated therewith) but not including inductance 5. Under this condition, the LC circuit I0, II being relatively high in capacity in effect provides nearlya short-circuit at the newhi'gher frequency and the proper excitation is supplied for the same higher frequency by inductances I4 and I5, plus the eifective impedance of the LC combination of inductances 1 and 8 shunted by condenser I 8.

If the highest frequency is desired, the wave change switch I 3 may be thrown to the right,

thereby shcrt-circuiting all of the plate inductances except coils l6 and ll'andthe frequency now generated will be determined by the constants of coils it and I1 with the tubes associated. At such frequency the condenser is acts substantially as a by-pass around inductances I and 8 and the excitation is furnished in effect by inductances l4 and i5. r

It will be understood that the-principle herein embodied may be applied to systems for generating a still greater number of frequencies, by increasing the number of sets of inductances and arranging the grid circuit-so that at each increase in frequency a new condenser begins to act substantially as a by-p-ass at the higher frequency, reducing viously effective in the grid circuit for producing excitation.

While-I have s own and described the circuit as being'of'the push-pull type, so -called, ormore strictly, the push-push type, and while this is the usually preferred form, it should be understood that my' invention is not limited thereto,

but may equally be employed in oscillating circuits of the tuned grid, tuned platetype employing only one tube,or a-group of tubes in parallel. If only one tube or group of tubes is used, it will be found desirable to provide aby-pass condenser around plate source l2, as will be readily understood, and the natural frequency of the oscillatory plate circuit with the tube or tubes in place determines the frequency of oscillation, while the grid circuit constants are so chosen, as already described, as to afford proper excitation at the various frequencies'without change of tuning in the grid circuit. I t

In the claims, I have used the term oscillatory circuit to designate the plate circuit, which is maintained in oscillathe driven circuit, and is tion at its own frequency (with the tubes associated therewith) and the term control circuit to designate the grid circuits, in the sense that the grid circuit controls the flow of plate current in the tubes, and not in thesense that the grid circuit controls the frequency of oscillation. This latter control isexercised primarily bythe oscillatory circuit. a

The term fixed tuned circuit is used to designate a circuit which operates at a frequencies without change of constants.

While I have shown and'described the'preferred embodiment of my invention, it will be understood that modifications and changes may be made without departing from the spirit and scope of my invention.

, I claim:

' 1'. In an oscillation generating system, in combination, an oscillator comprising a space current path, said path including a frequency-determining oscillatory circuit, means for selectively controlling the constants of said oscillatory circuit to select the frequency of oscillation thereof at one of a number of frequencies, a control circuit operating on said space current path, said.

the amount of inductance pre-' bination,

path, said path including a frequency-determinplurality of control. circuit comprising a fixed tuned inductance-capacity circuit. and inductance externalto said fixed tuned circuit 2. The combination claimed in claim 1, in

which said inductancecapacity circuit has a natural frequency lower than that of said external' inductance.

3. The ccmbinationclaimed in claim l, in' which the impedance of saidexternal inductance is insufficient tornaintain oscillation of the syssence of said inductance-capacity circuit.

4. The combination claimed in claim l, in which the impedance of said inductance-capacity circuit is insuificient to maintain oscillation of the system at the highest" selected frequency in the absence of .the said external inductance.

5..Iine combination clairried in claim 1, in

' which the impedance of said external inductance is insufficient to maintain oscillation ofthe system at the lower frequency in the absence of the inductance-capacity circuit, and in which the impedance of said inductance-capacity circuit is insufficient to maintain oscillation of the system at the higher frequency in the absence of'said external inductance. v I v 6. In an oscillation generating system, incombination, an oscillator comprising a'space current path, said path including a frequency-determining oscillatory circuit, means for selectively controlling the constants of saidoscillatory circuit to select the frequency of oscillation there- .ofat one of a number of frequencies, a

control circuit operating on said space current path, said control'circuit comprising a fixed tuned inductance-capacity circuit and, fixed inductance ex- 1 tern at the lowest selected frequency in the 'abternal thereto, the constantsof saidfixed tuned circuit and said inductances being so chosen that excitation is supplied to maintain the system in oscillation at any of the desired frequencies 'while' maintaining the control circuit constants unchanged. I

'Z. In an oscillation generating system, in comanoscillator comprising a space current to select the frequency of oscillation at any one a control circuit operatpaths, said control cirof several frequencies, ing on said space current cuit'comprisin'g a fixed tuned inductance-capacity circuit, an inductance external to said fixed tuned 4 circuit, a condenser shunting said external inductance and fixed tuned circuit, and affording oscillation-sustaining excitation at one of the chosenfrequencies, and by-passing said induct,-

-ance and fixed tuned circuit at higher frequencies, and additional inductance in said control circuit, external to the circuit formed by said fixed tuned circuit, said first external inductance and said shunting condenser.

ALEXANDER sENAUKE. 

